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Re: Stormbergia dangershoeki, new Early Jurassic ornithischian from South Africa



T. Michael Keesey

> ... and ceratopsians and pachycephalosaurs as derived ornithopods.  At
> least, that's how I read Butler's tree.

Depends on which definition of _Ornithopoda_ you are following. Sereno (1997) considered it a node-based clade, and anchored it on _Heterodontosaurus_ and _Parasaurolophus_ (1998), but in the latest edition of The Dinosauria, it is "all cerapodans closer to _Edmontosaurus_ than to
_Triceratops_", which explicitly excludes _Marginocephalia_.

Using Butler's tree, these two definitions give an Ornithopoda that are very different in content.


"Classic" Ornithopoda is a massively paraphyletic assemblage roughly equivalent to "unarmored
_Ornithischia_" or "bipedal _Ornithischia_". In adapting it to cladistic taxonomy, there seems to be a consistent desire to restrict it to a particular lineage (a la _Amphibia_) rather than expand it to include descendants (a la _Dinosauria_), probably because the very popular term "Ornithischia" is already available for the expanded group (not to mention "Predentata").

Yes, the traditional/classical Ornithopoda also included scelidosaurs, psittacosaurs and pachycephalosaurs. So I can't see why Ornithopoda shouldn't be node-based and expanded to include pachies and ceratopsians, should the topology show that iguanodontians and marginocephalians are closer than previously thought.


Cheers

Tim